Non-Square Cut - Shapeoko

CNC Machines Shapeoko
1

I am attempting to resolve an issue that has been persistent for a few months. After reading a few different threads and attempting several fixes, I decided it was best to check with the community.

Ultimately I can cut a small (4"x6") square, and it comes out perfectly square. I have checked this with a few squares. However, if I cut a larger square, (20"x30") square it comes out non square. To resolve this I have ensured my machine is square from corner, to corner per Winston’s videos. I have also ensured the wasteboard is leveled to the machine. The V-Wheels are properly secure, and I am using HDZ eccentric nuts with a little thread locker. My last attempt was to calibration my belts (steel core), I did this following the following thread: Measuring belt tension, squaring and calibration

I calibrated both of my Y-Belts to 123 Hz, however the distance from the Y-Rails to the front and back plates are not close like mentioned in the above thread. For example on the front left of the machine, I get a distance of 13.94 mm and the front right is 15.35 mm, a difference of 1.41 mm. To ensure my machine is square, I pulled the gantry, all the way to the front and both Y-Plates touch the front plates of the machine.

I may be answering my own question, but would you adjust the belts to different frequencies to ensure the distance between the front plates to the Y-Plates or equal? Or within a reasonable difference? This is the only thing I can think to try next, I just have been frustrated with this and want to ensure I am not missing anything. Below is some other information that may help.

  • I have tried adaptive cuts, with a finishing contour pass.
  • Material: MDF
  • Amana 46170
  • 17000 RPM (Makita)
  • 41 in/min
  • HDZ
  • Dust Extraction (Suck-it)
  • DOC: 1-2mm

Let me know if you need any other information

2

Interesting,

Are your Y rails the same length?

When your machine homes to the back, are the distances equal between the back of the Y plates and the rear frame of the machine?

3

DimensionsShapeoko

I apologize, I gave you the back dimensions in the original post, to give you the full picture here are the measurements I gathered. Also the right side, originally was at 123 Hz, which is why the measurements hardly changed, and the right side was 117 Hz, which was then “tuned” to 123 Hz.

I will go measure the Y-Rails, and see if there is an obvious difference between the two. Also, I triple checked the squareness of my machine, with the X Method yesterday and today. The difference between the two is about 1/32", which I thought was good enough. But I could be wrong?

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4

So it looks like you have an out of square of the X rail with the Y rails and frame of 1.4mm at the back and 1.1mm at the front then.

It’s worth checking the lengths of both the Y plates, the powder coat thickness could easily account for the 0.3mm here, or the Y rail lengths could be off.

It is also possible that the two Y belts have stretched differently but that is less likely if they’re from the same batch of belting.

I’d suggest checking the alignment of the Y plates with the ends of the X rail for squareness, that’s what left my machine with this skew. You can either shim the ends of the X rail to get it straight or you can take the nuclear option and actually square the thing properly;

IMG_8148
IMG_81482048×1536 687 KB

Mine looked like it had been cut to length on a wobbly chop-saw when I inspected it and only the lumpy high spots were making any contact with the Y plate. So I trimmed off the major lumps and got it within about 0.2mm with 400 grade on a flat block for final shimming.

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Thank you for your assistance on this, I just have a question or two to ensure I am understanding your correctly.

Are you saying the difference, of 0.3mm is how far out of square it is? I ask this, as you mention this may be accounted for within the powder coating of the Y-Plates. Or am I looking at a difference of 1.4 mm and 1.1 mm?

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6

Yep,

Sorry that was somewhat unclear.

Looking at your measurements, if we assume that the two Y rails are of equal length and form a square (which your corner-corner measurement suggests is a reasonable assumption within a few 10ths of a mm).

The X beam is off square by 1.4mm at the rear of the Y rails, that is forward 1.4mm on the right.

The X beam is then off square by 1.1mm at the front of the Y rails, forward by 1.1mm on the right.

This is largely good news as the offset is the same, the right end is forward and the left end backward.

So, there appears to be about 1.1mm of out of square to shim out on the ends of the X beam, inspect both ends to see if the Y plates are square with X, at least one of them is probably not square.

Then we have the 0.3mm which is likely due to some combination of;

  1. difference in tensioned belt length
  2. difference in Y rail length
  3. difference in Y plate dimensions (probably due to powder coat thickness)

Does that make any more sense?

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7

Yes that makes sense, I will spend a few hours tomorrow working through this to see if I can work this out.

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8

Do you have a suitable square for checking the ends and some shim stock?

If you don’t have shims then a good caliper and a stock of beer can / aluminium foil makes a decent working substitute.

Or you can go with this rather elegant solution for labelled shim stock;

9

I have aluminum foil, which I have used on the HDZ before. As for a square I have a few 1-2-3 blocks, and a quality combination square.

Also, thank you for your assistance. I believe you also produced a quality post/video about grounding the Shapeoko that I have been studying today. After I resolve this out of square issue, I may ask you a question that I have lingering about that.

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10

How far out of square is the large rectangle and in what manner. Is it possible that one of your Y belts has a bad spot?

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11

As far as I can tell, two or three of the corners are square. However, the one corner that I need to be square is out of square. Long story short, I purchased the Shapeoko to produce items for my small business, and I bought the XXL in hopes of cutting numerous items at once.

One of the items I have been working on requires double sided machining. To accomplish this, the item itself has two holes milled into the part, and a jig is cut, which holds ten of the items, with locating pins. So when I do the second side cut, I use the jig and I square it to my fence, which has been squared to the Shapeoko’s current “square”, using 1-2-3 blocks.

However, when I cut the jig I cut it from underneath so I can use metal inserts with threads for all of the hold downs I made using my 3D printers. So the corner that I use on the jig is the one corner out of square, so I can never get it perfectly square, meaning the second side that is cut, is misaligned. This is where I have begun this long journey into finding the issue and fixing it.

Tonight and tomorrow, I plan on checking everything I can for squareness and I take as many photo’s as possible. I squared this machine a year or so ago, and have had no problems until now. I will take a look at the belts, and everything else.

12

Maybe cut an 3x3 array of 10"x6" rectangles and see if the out of square is localized in the cutting envelope.

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13

The square issue is very minor, but one or two corners are not orthogonal basically. So if I place a square on the corner, one side or the other does not make contact with the square. It is really small, but enough to screw up double sided machining.

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If you are referring to the inside corner, it will not cut square with a round bit. You will need to use a file to square that corner.

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Can you measure the sides to determine if the opposite sides are parallel and the error is limited to the constant X or constant Y sides.

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I am talking outside cuts, which can create perfect 90 degree’s.

17

This morning a spent a few hours measuring, inspecting and checking the squareness of my Shapeoko. I will attempt to go through my findings clearly and as concise as possible. However, if you need more information or a different explanation, please let me know.

First I began with checking the corner to corner measurement of the frame. Here are the two measurements: Back Left to Front Right and Back Right to Front Left. I originally thought these two measurements, were close enough, anyone disagree?

I then did a quick test to see if there was a wobbly wheel, so I put my magnetic base with dial gauge on both Y-Plates. This can be seen here: Right Side Y-Plate. Doing this on both Y-Plates, found about the same error between the two, with no large jumps. So I believe my Y-Axis wheels do not have any defects.

After this, I measured the length of each Y-Axis Rail. I took these measurements from the back Y Plate, to the front of the Rail. Here are the photos of each side: Left Side, Right Side. Now my wife helped with these photo’s as the measuring tape would not stay without two hands. The Left Side picture was taken from a slight angle so the photo doesn’t do it justice, but it is slightly over 40.125 Inches, while the right side is right at 40.125 inches. To ensure the dimension of the Y-Plate did not effect these measurements, I measured both sides and each plate was 0.14 inches thick. So as far as I can tell, I have on Y-Rail that is slightly longer. We are talking like 0.2 mm - 0.4 mm longer.

I then wanted to double check my measurements from yesterday. Today this is what I have found:
DimensionsShapeoko

For some reason, today the measurements between the front and back plates are more agreeable. I then started looking at the squareness of the X-Axis to the Y-Axis. Here is the first photo, which shows the Right Side as seen from the front of the X-Axis. I set a machining square flat to the Y-Plate and as you see there is a slight gap. Which leads us to the second photo, which shows the left side of the X-Axis. The photo did not turn out great, but the left side of that photo is were the Y-Rail sits, and the top of the photo is the back of the machine, this shows a minor gap again.

When Liam mentioned my X-Axis was about 1.2 - 1.4mm out of square I was a little confused as I was pretty thorough with my initial squaring and setup of the machine. So the measurements and what I found today make more sense.

So the question then becomes is it worth trying to perfectly square the X-Axis to the Y-Axis? If so where would you shim? Here is a photo of how I numbered the four locations of the X-Axis, and the screw locations.
X-Axis

Hopefully someone can interpret my photos and help me. I am terrible with this, as it took my like 5 hours to tram my HDZ. I will conclude with some photos of the issue I am experiencing, here is a photo of my measuring the squareness of a piece of MDF I cut out: First Side, here I am holding the machining square flush with this side, and as you can see in this photo, the square does not sit flush with the otherside of the MDF square.

Let me know if I need to clarify anything.

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18

That’s as close as I got mine

That’s consistent with your data from yesterday then.

You’re now getting close to the repeatability limits of the X axis squareness on the Shapeoko (or what I think are the reasonable limits anyway).

The ‘problem’ is that the two Y axis steppers are run from the same step / direction signal on the controller and there’s just the one Y home switch. This means the machine can only run them in the relative position they’re in on power up and has to assume the X beam is normal to the Y when the home switch triggers.

On more expensive machines the two Y axes are driven separately by the controller and independently walked into a pair of home switches which can be trimmed to be square.

This is why you’ll frequently see the advice to manually roll the X beam backwards to hit the Y plates on the frame to square it before powering up.

The Y plates do a reasonable job of controlling the angle of the X beam but they can’t hold it perfectly straight.

I think what you’re seeing between yesterday and today is just the startup angle of the X beam being slightly different.

I have been considering putting a pair of adjustment bolts on the rear of my Y axes for the X beam to roll into on homing to ‘fix’ the homing, don’t know if that will work yet.

As above, I think we’re close to the ‘noise floor’ of the variation in position the X beam starts up in.

You clearly could get that to be squarer, it might be worth trying and you clearly are noticing the issue so it’s not pointless fiddling.

I shimmed mine by loosening off the bolts holding the X beam to the Y plates, loosening the Y plate V Wheel pretension to give wiggle room and inserting some shim either front or rear edge of the X axis.

It will not hurt anything to get that square, whether it will help or not is another question though.

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19

I was thinking the same thing, regarding my X-Axis just being misaligned with the front/back plates. Today I moved the X-Axis forward and back by hand a few times, which I believe reset the “squareness” of it to the Y-Axis.

I was aware of the single end stop issue, as I have worked thorough with 3D printers that have the same problem, using one steps/mm for Z-Axis and getting misalignment, etc. This could be the minor error I am seeing, so at this point before I start unscrewing bolts, and then re-tramming/surfacing my waste board after shimming, I will run another test cut and see if I get the same results on the same corner, then I will start the long and tedious process of shimming and squaring.

Also, I am not looking for perfection I just need all four corners to be square so I can set my jigs square to the machine.

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20

@LiamN

I was a little busy being Santa over the Holiday, but I finally got to a test cut this morning. It appears my issue has gone away, and the cause was the X-Axis losing square with the Y-Axis, due to only one side having an end stop.

@WillAdams

The new board used on the Pro, does it have room for two end stops on the Y-Axis?

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